Problems associated with simulated light sensitometry for low-crossover medical x-ray films

Over the past ten years the evolution of medical x-ray films has been toward films with reduced intensifying-screen light crossover in order to reduce blur and obtain higher spatial resolution. For films with very low crossover, misleading and incorrect sensitometric data may be obtained for film contrast evaluation and processor control if a simulated light sensitometer with a single-sided, light-exposing device is used. Screen light exposures were made using an inverse square, intensity-scale sensitometer. Simulated light exposures were made using a widely used single-sided, simulated-light sensitometer commonly used for film processor quality control, and a new simulated-light sensitometer capable of producing either single- or double-sided sensitometric exposures. The films used included one single-emulsion film and three double-emulsion medical x-ray films with light-crossover values ranging from approximately 3% to 30%. Sensitometric data showed a significant distortion (bump) in the characteristic curve for the 3% light-crossover film exposed with the single-sided, simulated-light sensitometer.